Are increased portion sizes to blame for Australia’s obesity epidemic?

If you had a hunch that restaurant desserts have been getting bigger in recent years, it’s not just you: scientists are sounding the alarm on larger portion sizes as a new major health threat.

This worrying trend has been pinpointed by experts as a major factor contributing to rising obesity rates in Australia. And many people are blissfully unaware that their weight gain has been caused in part by a gradual increase in portion sizes.

You might think that a piece of cake eaten ten years ago would be about equivalent to a piece of cake eaten today. But you’d be wrong. That’s because a measurable increase in average cake portions means a bigger calorie load relative to what it used to be, which also means a corresponding increase in weight gain.

So how much worse have things become? Well, to stick with our cake example, the upward drift in portion sizes means that a piece of cake you might eat today will likely contain about 1000 kilojoules more than it would have twenty years ago.

That’s a huge increase, because calories from cake are likely to represent excess energy in your diet, which will be stored as fat if you don’t burn it (and if it’s not excess energy that you’re getting from cake, your diet is probably not very nutritious).

Now consider that a kilogram of fat represents about 37,000 kilojoules of stored energy. That means if you eat cake once a month, after three years you’ll be about one kilogram heavier, relative to what you would have gained over a three-year period in the 1990s when portion sizes were smaller.

From one perspective, that’s great news: you’re getting more bang for your buck (assuming cake prices haven’t gone up by a corresponding amount relative to inflation). But what’s the motive on the seller’s side? Are they just catering to customers’ preferences? Or is it an insidious move to get people hooked on sweets?

And it’s not just sweets, by the way: average serving sizes for wine, pizza, and processed meat have also ballooned uncontrollably, increasing by nearly 70 percent over two decades.

So what’s the good news, if any? Well, some foods have actually gone down in caloric load over the same period of time. The average serving of fries is less fattening now than it used to be, for example. And servings for things like chocolate and beer are about the same as they were twenty years ago.

The lesson here? If you’re finding it hard to lose weight, or if you can’t figure out why you’re gaining weight, it might be due in part to a change in your diet that you weren’t even aware of.

But what if you want to lose weight and still eat cake? Well, you could just it less often, or cut it in half and take some home with you, but who wants to do that? Possibly the best option of all: bake your own, which allows you to determine the calorie content and portion size.

Because when else can you use weight loss as an excuse to make chocolate cake at home?

Let’s just hope that portion sizes of wine continue to increase. That’s one thing we can all get behind.